1. Field of the Invention
The present invention relates generally to electric arc lamps, and more specifically to pressurized gas types that can operate at power levels in excess of a kilowatt and have a very small, stable point of radiation.
2. Description of the Prior Art
Texas Instruments (Austin, Tex.) introduced the digital micromirror device (DMD) in 1987. The DMD is a micro-electro-mechanical systems (MEMS) that digitally controls thousands of tiny mirrors in an array on a semiconductor chip. The MEMS structure is fabricated by complementary metal oxide semiconductor (CMOS) technology processes over a CMOS memory. Each light switch has an aluminum mirror that reflects light in one of two directions, depending on the electronic state of the underlying memory cell. Video images can be projected by shining a powerful light on the DMD and electronically tilting individual mirrors to form whole images on the array. Bursts of digital light pulses with various durations are interpreted by the eye as shades of gray. Color filters are used in combination to create full-color projected images.
Digital light projection (DLP) systems include image processing, memory, a light source, and optics. A typical DLP system is capable of projecting large, bright, seamless, high-contrast color image with better color fidelity and consistency than traditional types of displays.
When a DMD memory cell is in the 1-state, the mirror rotates to its +10 degree position (relative to zenith). In the 0-state, the mirror rotates to its xe2x88x9210 degree position. In the DMD, a suitable light source and projection optics are arranged so the mirror can reflect incident light either in or away from the pupil of a projection lens. Typically, the 1-state of the mirror produces a pixel that appears bright on the screen, and the 0-state of the mirror appears dark. Gray scale is achieved by binary pulse-width modulation, e.g., tilting the mirror to the 1-state for different time durations according to the brightness shade needed. Color pixels can be generated by using stationary or rotating color filters, in combination with one, two, or three DMD chips.
The DMD light switch is a MEMS structure consisting of a mirror that is rigidly connected to an underlying yoke. The yoke in turn is connected by two thin, mechanically compliant torsion hinges to support posts that are attached to the underlying substrate. Electrostatic fields developed between the underlying memory cell and the yoke and mirror cause rotation in the positive or negative rotation direction. The rotation is limited by mechanical stops to +10 or xe2x88x9210 degrees. The fabrication of the DMD superstructure begins with a completed CMOS memory circuit. Through the use of six photomask layers, the superstructure is formed with alternating layers of aluminum for the address electrode, hinge, yoke, and mirror layers and hardened photoresist for the sacrificial layers that form the two air gaps. The aluminum is sputter-deposited and plasma-etched. The sacrificial layers are plasma-ashed to form the air gaps.
Texas Instruments is actively pursuing two broad business opportunities for DLP, projection displays and continuous-tone color printing. Projection displays are needed for large audiences, portable business uses, and consumer/home appliances.
Digital display engines (DDE""s) are now being marketed that include a DLP subsystem ready for integration with a video interface, a power supply, a sound sub-system, controls, and a cabinet Texas Instruments is manufacturing DDE""s for business projectors with VGA resolution (640xc3x97480). SXGA resolution (1280xc3x971024) have also been demonstrated.
Unfortunately, the prior art in high-intensity lamps lack the particular kind of light source needed for good DPL systems. The arc needs to be short and very stable. But in conventional lamps, the arcs are relatively long and jitter. This makes less than all the light produced available to the DMD and the image on the display screen.
Prior art attempts at very-short arc lamps with solid cathodes and anodes have resulted in the two expanding and colliding under the heat of operation.
It is therefore an object of the present invention to provide a high intensity lamp suitable for DLP systems.
It is another object of the present invention to provide an arc lamp with a small, stable arc during operation.
It is a further object of the present invention to provide an arc lamp that pumps its internal pressurized atmosphere through the arc and out vents in its anode structure.
Briefly, a high-intensity arc lamp embodiment of the present invention comprises a glass envelope with a pressurized gas atmosphere. A cathode and an anode structure are disposed within. A pointed tip of the cathode is juxtaposed by a central hole in a face of the anode and a gap between them is on the order of 0.050 inches. Such central hole is vented away from the arc down inside the anode structure. Furthermore, the central vent hole prevents a physical-contact collision between the anode and cathode during the heat of operation. During operation, heat from the arc at the entrance to the central hole drives a wind of xenon gas down through such vents in the anode structure.
An advantage of the present invention is that an arc lamp is provided that can operate at kilowatt power levels and has a long operational life.
Another advantage of the present invention is that a light source is provided which is suitable for DLP systems.
A further advantage of the present invention is that an arc lamp is provided with a very small point of light source that is also very stable during operation.
These and other objects and advantages of the present invention will no doubt become obvious to those of ordinary skill in the art after having read the following detailed description of the preferred embodiments which are illustrated in the various drawing figures.